I recently read an extremely thorough paper looking into the existing research on intermittent dieting and some theoretical ways this could be applied for athletes looking to lose fat and maintain, as much as possible, resting energy expenditure, performance, compliance, and muscle mass.
The paper is “Intermittent Dieting: Theoretical Considerations for the Athlete” by Jackson James Peos, Layne Eiseman Norton, Eric Russell Helms, Andrew Jacob Galpin, and Paul Fournier. You can google the title and have full access to the paper. The paper is incredibly specific and covers many topics. For the purpose of this review I will keep things as simple as possible and list some of my favorite take-away points.
Dieting down or cutting weight for competition
Athletes have used a number of methods to lose body fat, or lower body weight prior to competition (bodybuilding show, making weight for a fight/powerlifting meet/weightlifting meet). Of those methods, the most commonly used is continuous energy restriction (CER). This method is simply lowering your total calories below maintenance everyday until the goal weight or body fat percentage is reached. From their deep dive into the existing research they believe there may be a better way. They believe using an intermittent energy restriction (IER) approach, switching between eating at energy restriction for multiple weeks and eating at energy balance for 1-2 weeks (refeed/refuel periods).
The body’s responses to energy restriction
The authors explain the general adaptations the body goes through during periods of energy restriction. The body has a way of fighting back when you begin to cut calories. Your body wants stay at homeostasis and will express a few mechanisms that make it difficult to stay on track during energy restriction. An adaptation we aim to minimize is the lowering of resting energy expenditure (the calories you burn to keep the body alive). As this lowers your body will naturally burn less calories throughout the day, making it difficult to stay on track. Another adaptation we want to minimize is the loss of free fat mass i.e. muscle. As we lose muscle we can start seeing decreases in performance. This paper suggests IER is a better way to keep more resting energy expenditure and muscle.
Appetite and energy restriction
Two hormones leptin and ghrelin regulate your appetite. During periods of energy restriction leptin and ghrelin will increase appetite. This hormone reaction and increase of appetite strongly correlated with fat loss and a lower resting energy expenditure. This increase in appetite raises the difficulty of CER for more than few weeks. Refeed periods in the IER protocol may have an effect in lowering this response from energy restriction periods.
Intermittent Fasting vs. Continuous Energy Restriction
Under the umbrella of IER is the popular Intermittent Fasting (IF) protocol. For those who don’t know what this is it has scheduled windows of time to eat and fast. The commonly used window is a 16 hour fast followed by an 8 hour feeding window. A recent review of multiple studies comparing IF and CER in overweight people found that “all studies had comparable reductions in body weight where overall energy intake was matched”. So when total calories were equated between groups they experienced the same results whether they were using IF or CER. As the IER protocol lacks a clear definition, IF still relates to it but does not seem to work better than CER. IER differs in the use of the longer phases of energy restriction for 2-3 weeks followed by a 1-2 week refeed at energy balance. The equal effect between IF and CER may be due to the use of equal calories consumed each day but with an added window of fasting. It’s still the same routine everyday of energy restriction for several weeks.
Intermittent Energy Restriction vs. Continuous Energy Restriction
For the short term use, 1-2 weeks, IER and CER brought about similar results. However, for long term use over several weeks, 8-16 weeks, IER showed more fat loss and a higher retention of resting energy expenditure. One of those studies had a group on CER for 8 weeks and the other group ate two weeks at energy restriction and two weeks at energy balance for 16 weeks. An issue here could be the length of the IER at 16 weeks but it still brought about better results. Another study had a group on CER for 8 weeks and the other cycle between energy restriction for one week and one week on their habitual diet (no prescribed ER) for 8 weeks. Equal weight loss was achieved between the groups, but the interesting point to look at is the time spent at energy restriction. CER spent all 8 weeks in energy restriction while the IER group only spent 4 weeks. Meaning the IER had better weight loss efficiency.
The use of the refeed period may be holding back some the bodies reactions to energy restriction. During a refeed phase it is suggested that the appetite regulating hormones are suppressed, resting energy expenditure can be better preserved, and muscle can be refueled with a higher glycogen storage. From this we hope to mitigate decreases in performance for the athlete.
To better understand the use of long term IER, Peos and colleagues will be examining the use of three week blocks of energy restriction followed by one week of eating at energy balance over 15 weeks.
Recommendations of Implementation
The authors provide a few guidelines to follow if you would like to try this out. They mention that more research is needed before they can completely prescribe this plan as superior to other forms of energy restriction. But if you’d like to experiment with yourself then here’s a few safe suggestions.
-Avoid severe IER and/or rapid weight loss. Drastically cutting too many calories below maintenance will increase loss of muscle, decrease performance, increase fatigue which can lead to risk of injury. Use a moderate approach to energy restriction aimed at a bodyweight loss of 0.5-1% per week. Athletes can reduce energy intake to a max of 35% relative to energy intake needed for maintenance.
-Use resistance exercise to maintain as much muscle as possible. The goal of the athlete during this period is to minimize any decreases in performance. This will also help maintain resting energy expenditure which could increase fat loss efficiency.
-The duration of energy restriction and refeed periods. Off the limited research they recommend a conservative cycle of alternating two weeks of moderate energy restriction with two weeks in energy balance/maintenance.
-Coordinate refeeds with training. The higher calorie weeks can line up with outcome-focused and high volume training periods.
-Maintain a higher protein intake in order to reduce muscle loss, maintain higher energy expenditure from the thermic effect of food. A recommendation of 2.3-3.1 g/kg of lean body mass. This equates 2.0-2.6 g/kg of absolute body mass of an 80 kg athlete with 15% body fat.
-Emphasize carbs during refeeds. The article further explains why the athlete should emphasize carbs for performance purposes. Leptin levels are higher after carb feeding which lowers appetite and can help with compliance of the diet. Combining the higher carb refeed with resistance training may have a better anabolic response.
Having the refeed periods may also bring about a mental break from the energy restriction periods. It can lower the mental and physical fatigue that builds over a few weeks. I compare it to a deload week in training. You push your body to adapt and grow for around three weeks before you take a deload week for physical and mental restoration. When you come back you feel rested and ready to ramp things up again. During the refeed phase your metabolism has a chance to re-energize, refuel, and prepare for more. Mentally you get to eat some more (which is awesome) and feel that extra energy throughout the day and in the gym.
If you have questions or want more information about how you can safely lower your body fat reach out!
Special thanks to the authors of this paper as well as all the contributors that helped put it all together.